EVALUATION OF CORROSION INHIBITION PROPERTIES OF POLYANILINE (PANI) MODIFIED EPOXY RESIN PREPARED AT DIFFERENT CURING TEMPERATURE

In this work, epoxy resin prepared from Epikote 828/m-XDA system was modified with polyaniline (PANI) and used as corrosion resistant surface coatings for carbon steel. The aims of this study were to evaluate the performance of PANI modified epoxy coatings in inhibiting corrosion. Various concentrations of polyaniline emeraldine salt (PANI-ES) particularly 0.5, 1.0 and 1.5 wt. % were incorporated in the epoxy coatings to enhance the corrosion resistant. In addition, these epoxy coatings were cured at two different curing temperatures: room temperature (RT) and 120° C respectively. Curing is an important process as it will determine the properties of the formed epoxy resin network which in turn will affect its performance. An epoxy resin needs to be fully cured to attain good chemical and mechanical properties thus enabling maximum performance. Coatings containing polyaniline were then characterized using Differential Scanning Calorimetry (DSC), Fourier Transform Infrared (FTIR) and Thermal Gravimetric Analysis (TGA). The corrosion inhibition properties of the coatings towards the steel were also evaluated in various analysis and corrosion tests such as salt spray test, water absorption test and electrochemical impedance spectroscopy (EIS). The adhesion strengths of the coatings were determined by the pull-off test and digital microscope was used to analyze the morphologies of the coated carbon steel. The results obtained from these corrosion analysis and tests will be correlated to develop better understanding on the corrosion behavior. The IR spectra obtained from FTIR analysis confirmed both structures of unmodified and modified epoxy. Based on the DSC and TGA analysis, results obtained revealed that the glass transition temperature, Tg and thermal stability of modified epoxy were higher as compared to unmodified epoxy system. The epoxy modified with 0.5 wt. % PANI and cured at 120° C, exhibit the highest values of Tg and thermal stability among all samples. Results from water absorption test, pull-off test and salt spray test also show that the modified epoxy with 0.5 wt. % PANI, cured at 120° C absorbed less water, display higher adhesion strength and provided the best corrosion resistant to the steel than the unmodified epoxy system. For salt spray test, several corrosion characteristics such as blistering, delamination and rusting were observed after 30 days exposure where carbon steel plates coated with unmodified epoxy showed more severe corrosion characteristics than those coated with modified epoxy. The values of corrosion rates obtained from EIS also revealed that modified epoxy coatings display better corrosion protection performance towards the steel than unmodified epoxy coatings where lower values of corrosion rates were obtained. This is also supported with the higher charge transfer resistance (Rct) and lower double layer capacitance (Cdl) values obtained after 30 days of immersion in 3% NaCl. Based on the results obtained, it can be concluded that modified epoxy coatings provided better corrosion resistant towards steel where 0.5 wt. % PANI, cured at 120° C exhibit the best performance among all samples.